This invention relates to a multi-screen projector which comprises a plurality of unit projectors and a multi-screen formed by a combination of unit screens corresponding respectively to the unit projectors. More particularly, the invention relates to a mounting mechanism for enabling a vertical adjustment of the position of the multi-screen and for enabling a horizontal movement of the multi-screen, and also relates to the construction of a transmissive screen.
A multi-screen projector is a projector having an enormous screen formed by arranging unit projectors in n rows in a vertical direction and in m columns in a horizontal direction (n and m are arbitrary numbers). FIG. 1 shows a multi-screen projector with two rows and two columns of unit projectors. In FIG. 1, reference numerals 1, 2, 3 and 4 denote the unit projectors, respectively, and reference numerals 5, 6, 7 and 8 denote transmissive unit screens, respectively.
Conventional multi-screen projectors have been a mere stack of ordinary unit TV projectors for home use which are combined with unit screens. Therefore, as shown in FIG. 1, a non-transparent structural body, formed as a result of connecting the adjacent unit screens together, has been present in a shaded part 9 (the default band along the peripheries of the unit screens). As a result, a shadow due to the non-transparent structural body has been unavoidable in that portion of the enormous screen on which a picture image is desired to be displayed. When the unit screen is about 800 mm wide, the width of the shadow has been about 8 mm or more, i.e., 1% or more of the width of the unit screen. Since the pixel size for a unit TV projector is about 0.2% of the width of the screen unit, the above shadow whose width is 1% or more of that of the unit screen is equivalent to about 5 pixels or more.
FIG. 2 shows a typical construction of a unit screen with the diagonal about 40 inches. FIG. 2 is an example of a two-sheet construction. As viewed from the observer's side, a Fresnel sheet 11 is disposed at the back side of the unit screen, and a front sheet 12 is disposed at the front side. The Fresnel sheet 11, about 3 mm thick, converts incident light, coming in a macroscopically diverging manner from a projection lens (not shown in FIG. 2) behind it, into collimated projection light. The Fresnel lens, in other words, functions the same way as a single convex lens.
The front sheet 12 comprises vertical lenticular stripes 14 and vertical black stripes 13. The lenticular stripes microscopically diffuse the light in the horizontal direction, that is, increases the horizontal directivity angle. A detailed example of its construction is described in U.S. Pat. No. 4,536,056 filed by the inventor of the present invention.
FIG. 3 shows a lenticular sheet 16 which diffuses the light in the vertical direction. As shown in FIG. 3, horizontal lenticular stripes are formed on its light incident surface and light-outgoing surface so that the light can be microscopically diffused in the vertical direction. The lenticular sheet 16 is interposed between the Fresnel sheet 11 and the front sheet 12 (both of which are shown in FIG. 2), and thus these three sheets jointly constitute a three-layer sheet.
Incidentally, there has also been used another method in which the lenticular lens 16 is not used, and instead diffuser elements (e.g. particles of SiO.sub.2) which diffuse the light microscopically and randomly are admixed with the front sheet 12 of FIG. 2.
Each of the three sheets 11, 12 and 16 shown in FIGS. 2 and 3 is composed of a transparent resin belonging to a methacrylic resin or a polystyrene resin. Therefore, they expand and contract according to the ambient temperature, and their temperature coefficient is about 60 PPM/.degree.C.
These sheets also expand and contract according to a change of the ambient humidity, and the line expansion rate is about 400 PPM for the methacrylic resin-type sheet and about 100 PPM for the polystyrene resin-type per 10% increases of the relative humidity.
Sometimes, a change in humidity, due to the large time constant, is transiently responded by an unbalanced state of a water absorption profile of the sheet in the direction of the depth thereof. In such a case, there has been encountered a problem that the front sheet 12 is deformed into a curved shape. To overcome this problem, it has been necessary in the prior art to retain each unit screen by a frame provided at the shaded part 9 of FIG. 1 and along the outer peripheral edge of the overall screen. Therefore, a shadow of a great width has unavoidably been produced at the joint portion (boundary band) between any two adjacent unit screens.
Japanese Patent Unexamined Publication No. 1-134491 discloses a construction in which right and left edge portions of a screen are fastened by screws. This construction has a drawback that the shadows of the screws appear on the display screen, so that important information fails to be displayed.
In conventional devices, as disclosed in Japanese Patent Unexamined Publication No. 1-134491, the problem has been dealt with by increasing the size of the through holes (for mounting the screen) or by applying a resilient pressing means to an upper hanging portion. In the prior art, no problem has been encountered when two columns of unit screens are used; however, in the case of several columns of unit screens, the multi-screen expand and contract to a greater degree, so that this could not be dealt with.
In a conventional n-row multi-screen, it is necessary to vertically arrange n rows of Fresnel sheets (which constitute a screen) between a front sheet and a reinforcing sheet. However, since a concentrically-shaped Fresnel lens is formed on one surface of the Fresnel sheet, the n rows are not constituted by a single sheet, and generally the n rows are constituted by n sheets. Therefore, when the n rows of Fresnel sheets 22 are attached by screws 25 to the reinforcing sheet as shown in FIG. 4, the shadows of the screws 25 are displayed on the display screen, thus adversely affecting the picture.
In a multi-screen of the n-row and m-column type, the size of the overall screen is very large, and it is difficult to obtain the precision of the mounting portions. However, unless the n-row and m-column screen is accurately arranged, a spacing is formed between the m columns of screens, or a vertical step is formed between the n rows of screens, so that the picture is affected at the boundary band between the adjacent screens.
Also, the size of the multi-screen becomes very large. For example, when the unit screens of 50-inch size are arranged in four rows and four columns, the size of the overall screen is 3.5 m in height and 4.2 m in width, and the amount of expansion and contraction due to a temperature change is as large as about 10 mm. Therefore, when the screen is fixed by the screws, the screen is broken or corrugated due to the expansion, thus greatly affecting its performance.
In order to minimize the above shadows, the inventor of the present invention has already filed a patent application directed to the construction shown in FIG. 5.
FIG. 5 shows two of units screens composing a multi-screen. In FIG. 5, reference numeral 11 denotes the same Fresnel sheet as the Fresnel sheet 11 in FIG. 2. The size of this sheet is about 40-inch size, that is, 800 mm in width, 600 mm in height and about 1 to 3 mm in depth. As shown in FIG. 6, the Fresnel sheet in an unloaded state has a one-dimensional curvature such that the Fresnel sheet is curved or warped toward the observer's side. It is known that such one-dimensional curvature can be imparted to the Fresnel sheet by forcibly applying a one-dimensional curvature to an ordinary planar Fresnel sheet and then by leaving the thus curved Fresnel sheet in an environment of a plastic deformation temperature of about 80.degree. C. or higher. As later described in detail, the radius of the one-dimensional curvature is determined to be about 10 to 30 m.
Reference numeral 21 in FIG. 5 denotes a hole formed in the Fresnel sheet 11, and reference numeral 22 denotes a wire. The material for the wire 22 is metal such as stainless steel or a plastics material such as nylon. The wire may be a single wire or be made of twisted strands, but the outer diameter of the wire is smaller than the size of a pixel on the display screen. Each wire 22 passes through the holes 21, and applies a tension to the Fresnel sheet 11 at least in a direction to bind the Fresnel sheet 11 to a reinforcing sheet 20.
Reference numeral 23 denotes a coil spring which is usually made of a metal wire. Reference numeral 24 denotes a rigid support body, and is made of metal or a plastics material. Each coil spring 23 is supported at one end on the support body 24, and applies a tension to the corresponding wire 22. This tension is transmitted to the Fresnel sheet 11 via the wire 22 so as to bind the left edge of the Fresnel sheet 11 to the reinforcing sheet 20.
The rigid support body 24 is located in a free space or region not to cause any shadow on the screen. This free space is shown in FIG. 9.
Although only the supporting structure for the left edge of the unit screens is shown in FIG. 5, the same structure is also applied to the upper, lower and right edges of the unit screen, though this is omitted in FIG. 5 for the simplicity of the illustration.
Note that at each of the upper and lower edges, the wire 22 passes through holes 25 formed through the Fresnel sheet 11 and the reinforcing sheet 20. Although many holes 25 are provided, only one of them is shown in FIG. 5 for illustration purposes.
FIG. 7 is a perspective view of the structure of the completely connected-type left edge of the combination of an elongated front sheet 12, the reinforcing sheet 20 and the Fresnel sheets 11 both of which are shown in FIG. 5. Reference numerals 22, 23 and 24 denote a wire, a coil spring and a support body, respectively. Reference numeral 21 denotes a hole formed in the Fresnel sheet 11 and the Fresnel sheet 11. Each wire 22 passes through the holes 21, and is extended along the side surface of the reinforcing sheet 20, and is connected to the coil spring 23. Therefore, the tension of the coil spring 23 applies component forces to the front sheet 12 and the Fresnel sheets 11 so as to bind them to the reinforcing sheet 20.
Although only the left edge portion of the supporting structure is shown in FIG. 7, the same structure is used at the right edge portion. Reference numeral 25a denotes a hole formed through both the front sheet 12 and the reinforcing sheet 20. A threaded rod (not shown) is extended through the hole 25a, so that the front sheet 12 is fixedly hung on the reinforcing sheet 20. Although not shown in FIG. 7, the upper and lower edges of the Fresnel sheet 11 are supported by the wires passing through the holes 25a described above in FIG. 5.
FIG. 8 shows a conventional multi-screen. In FIG. 8, reference numeral 20 denotes an elongated reinforcing sheet for each column, and reference numeral 12 denotes an elongated front sheet for each column, and reference numeral 11 denotes a Fresnel sheet of about 40-inch size. Although not shown in this Figure, the supporting structures between these sheets are as described above.
The above conventional construction has a problem that in the event of an earthquake, the reinforcing sheet 20 is much swung in a direction perpendicular to the plane of the screen. Another problem is that due to variations in warp or curvature of the reinforcing sheets, some parts of the screen are displaced out of position in forward and backward directions, thus detracting from the appearance. Further, in order to support the weight of the Fresnel sheet 11, the through holes 25a are formed through the reinforcing sheet 20, and the thin wires are passed through these holes, respectively; however, this operation can not be carried out easily. A further problem is that each hole 25a causes its shadow to appear on the picture. Furthermore, it has been desired to further decrease the discontinuity of the picture at the boundary band between the adjacent unit screens.